1. Field of the Invention
The present invention relates generally to a bicycle shifter which is easy to control gear shifting with less force.
2. The Prior Arts
A conventional derailleur device for a bicycle generally includes sprocket wheels on the rear wheel axle, a chain connected between one of the sprocket wheels and the chain wheels, a derailleur located close to the rear wheel and a shifter mounted to the handlebar of the bicycle. The shifter is connected to the derailleur by a cable such that when rotating the shifter, the cable can be extended or retracted to shift the chain from one sprocket wheel to another one to achieve the purpose of gear change.
The shifters are usually classified into a twist style and a trigger style so that the user can rotate the twist-style shifter or move the trigger-style shifter to control the gear shifting. Most of the shifters have an index mechanism which provides the shifter with discrete stops. Each stop corresponds to one position of the derailleur. This allows the cyclist to know the shifter is precisely operated to a specific gear ratio. Usually, the conventional index mechanism includes an elastic member that has an extension arm and an elastic portion protruded from the extension arm. The elastic portion is movably engaged with inner teeth located at the inner periphery of a casing of the shifter. When rotating the handle or moving the trigger, the elastic portion moves over the inner teeth to generate sound and is positioned at one of the concaves between the teeth. However, when changing the gear ratios, the cyclist needs to apply a force larger than the friction force between the elastic portion and the inner teeth. The forces to shift gears at low gear ratios are different from those at high gear ratios. At some gear ratios, it needs a large force to shift gears, which is likely to make the elastic member accidentally jump over several teeth. Moreover, the force applied by the cyclist has to be large enough to slightly deform the elastic member such that the elastic member can moves from one concave between two inner teeth toward next concave. However, the elastic member engages with the inner teeth at one side only. Thus, it is more likely to happen that the elastic member jumps over several teeth at a time.